Global vs. Local

But sometimes it does

• Sometimes you will see is instead of ==.

1 == 1.0
1 is 1.0

True

False

Conditional statements

The important question of what to do “if” something happens.

• Programming languages are languages
• if something is True
  • you should do something
• else
  • do something else

if *statement*:
    print("the *statement* is true")
else:
    print("the *statement* is false")

Multiple if-statements

value = 3
1if value == 1:
    print("the value is 1")
2elif value == 2:
    print("the value is 2")
3elif value == 3:
4    print("the value is 3")
else:
    print("the value is something else")

the value is 3

Short forms for conditionals

amplitude = 24
is_action_potential = "is AP" if amplitude > 0 else "no AP"
print(is_action_potential)

is AP

How to check if everything is true?

• Validate all the statements in a list

everything_is_true = [True, True, True]
something_is_true = [True, False, False]

all(everything_is_true)
all(something_is_true)

True

False

any(everything_is_true)
any(something_is_true)

True

True

For loops

for *element* in *iterable*:
    *body*

• iteration is the repetition of a process until a specific condition is met
• what’s iterable?

# calcualte a sum
list_to_sum = [2,3,4,5,7]
num_sum = 0
for val in list_to_sum:
   num_sum = num_sum + val

TO DO

Given:
A = [3, 4, 5, 9, 12, 87, -65, 300, 450, -32]

Use for loops to:
1. Add 3 to each element of the list
2. Calculate the average of the list, but negative values are calculated as 0s
3. Find the maximum value
4. Find the index (position) of the max value

Index based for loops - range()

for i in range(5):
    print(i)

0
1
2
3
4

# looping through data indices. find the max
B = [1, 4, 6, 7, 89, 54]
big_indx = 0
for i in range(len(B)):
    if B[i] > B[big_indx]:
        big_indx = i
print('The max value in B is', B[big_indx], 'found on position', big_indx)

The max value in B is 89 found on position 4

Index based for loops - enumerate()

• assigns a count to each item within an iterable and returns it as an enumerate object
• one way to avoid nested loops

import numpy as np

array_a = np.arange(20, 25)
for indx, val in enumerate(array_a):
    print('the index is', indx)
    print('the value is', val)

the index is 0
the value is 20
the index is 1
the value is 21
the index is 2
the value is 22
the index is 3
the value is 23
the index is 4
the value is 24

Break and continue statements

• break - immediately terminates the loop
• continue - skips whatever is after it and continues with the next iteration
  • mostly used after a conditional statement

Let’s wait while we wait

• Start a little counter

import time
counter = 0
while counter < 10:
    time.sleep(1)
    counter += 1
    print("You waited for " + str(counter) + " seconds...")

• Good for keeping processes running

Errors and how to read them

There are useful resources regarding errors

• Simply googling works surprisingly well
• You will often end up on stackoverflow
  • There is no question which was not already asked¹

Types of errors

1. SyntaxErrors
2. IndentationError
3. NameError
4. TypeError
5. IndexError
6. AttributeError
7. etc.

Fix errors

• Breath
• Don’t panic
  • Identify the error by checking the terminal output
  • Look at the line provided
  • Go backwards if error is nested